In the industrial field of the image forming apparatus, the structure detachably provided with a belt unit such as a carrier belt and an intermediate transfer belt has been supplied. Prior image forming apparatuses included a structure provided with the belt unit so as to be detached from one side of the main body through the linear sliding motion performed by the slide mechanism. The detachment of the belt unit from one side allows the access to the belt unit therefrom. In the case where it is difficult to access the belt unit from the top, for example, a large component is provided above the belt unit, or the image forming apparatus is desired to be used while avoiding the access to the belt unit from the top, the aforementioned structure is advantageous.
If the unit as the above-structured belt unit is detachably provided to the main body by merely sliding such unit linearly with the slide mechanism, the unit is required to be sufficiently held so as not to be dislocated from the position where it is installed. The mechanism for retaining the unit or the slide mechanism may enlarge and complicate the structure.